This invention relates to differentials of the type including planetary gearing for heavy duty vehicles More particularly, the invention relates to locking differentials for axle shafts.
Most "planetary" differential assemblies employed in heavy duty vehicular operations are utilized in gear reduction applications, such as transfer cases. It has not been common practice to employ planetary differentials in axle applications, where torque is split on a 50--50 basis. Thus, standard rear driving axles of almost all heavy trucks are "beveled" gear differentials similar to those provided in passenger cars.
Where, however, "non-standard" planetary differentials have been utilized in rear drive axles of trucks, such differentials have typically incorporated an electromagnetically actuated limited slip function, utilizing friction plates. In some designs, the friction plates can be selectively engaged to "positively" lock the coaxial shafts together, resulting in avoidance of differential action on demand, such as when the vehicle is traveling over slippery roads during inclement weather conditions, for example.
A major drawback, however, is realized when the friction plates become worn under the numerous cycles of electromagnetic actuation which occur during their useful lives. After such wear, the ability of the operator to positively lock the vehicle becomes somewhat "less than positive". A preferred system would establish a truly "positive" lock; one not relying on friction plates which become worn and thus lose effectiveness in normal operations.